首页博文目录关于我

个人资料

微博

加好友发纸条

写留言加关注

博客等级：
博客积分：

博客访问：
关注人气：
获赠金笔：0支
赠出金笔：0支
荣誉徽章：

正文字体大小：大中小

r 打开.nc 文件

(2015-11-26 01:54:03)

标签：

r

.nc

netcdf

分类： SAS_STATA_GAMS_MATLAB_Hadoop

How to Read Data in netCDF Format with R

Overview:

R is a software package for statistical computing and graphics. Data in netCDF format can be imported to R by using netCDF-enabled R-packages. This recipe shows how to import a gridded data file by using either of two R-packages, RNetCDF and ncdf.

Best When:

The data is in CF-complaint netCDF format. We suggest the use of R 3.0 or later.

Task:

Viewing Data

Example:

This example shows how to import a data file from Tropical Rainfall Measuring Mission (TRMM) 3-hourly precipitation into R.

Procedure:

1) Getting a data file in netCDF format


The original data format of TRMM products is the Hierarchical Data Format (HDF).  There are a number of ways to obtain the data as a CF-compliant netCDF file from the Goddard Earth Sciences Data and Information Services Center (GES DISC).  In this example, the 3-hourly TRMM data at 2006-01-01T03:00:00Z was downloaded from OPeNDAP service at the following location:


http://disc2.nascom.nasa.gov/opendap/hyrax/ncml/TRMM_L3/TRMM_3B42/2006/001/3B42.20060101.03.7A.HDF.Z.ncml.html


Clicking on the “Get as NetCDF” button to download the file as:


 nc_3B42.20060101.03.7A.HDF.Z.ncml.nc

2) Installing R-packages


Download and Install R-base first from r-project, if R is not already installed. In this example, Windows R 3.1.2 and Linux R 3.1.2 are used.


(We found that the instructions at the Ohio State University (http://www.stat.osu.edu/computer-support/mathstatistics-packages/installing-r-libraries-locally-your-home-directory) are helpful for the  installation process.)

Install netCDF enabled R-packages:

ncdf : This is a R interface for handling netCDF. In this example, ncdf_v1.6.8 is used. For data in netCDF4, an R-package, ncdf4, is available.

RNetCDF : This is another R interface to handle netCDF . In this example, RNetCDF_v1.6.3-1 is used.

Install R-packages for plotting images:

fields: Tools for handling spatial data.

maptools: Tools for reading and handling spatial objects

3) Importing data

Start R
Example-1: Read the data with the R-package “RNetCDF”

(Save the following as a R script file )

#Change to your working directory

setwd("C:/Downloads/data")

#Load package RNetCDF

library(RNetCDF)

#Open data file (TRMM 3-hourly )

fname<-"nc_3B42.20060101.03.7A.HDF.Z.nc"

fid<-open.nc(fname)

#Print dataset summary information (see Figure 1)

print.nc(fid)

#Read data

dat<-read.nc(fid)

z<-dat$precipitation

ylat<-dat$nlat

xlon<-dat$nlon

#Close file

close.nc(fid)

http://disc.sci.gsfc.nasa.gov/recipes/sites/default/files/media/recipe-R01_fig1(1).png打开.nc 文件" />

Figure 1: Sample file metadata from R-package “RNetCDF”.

Example-2: Read data with R-package “ncdf”

(Save the following as a R script file)

#Change to your working directory

setwd("C:/Downloads/data")

#Load package ncdf

library(ncdf)

#Open file ( TRMM 3-hourly )

fname<-"nc_3B42.20060101.03.7A.HDF.Z.nc"

fid1<-open.ncdf(fname)

#Print dataset summary information (see Figure 2)

print.ncdf(fid1)

#Read data

z<-get.var.ncdf(fid1,"precipitation")

ylat<-fid1$dim$nlat$vals

xlon<-fid1$dim$nlon$vals

#Close file

close.ncdf(fid1)

http://disc.sci.gsfc.nasa.gov/recipes/sites/default/files/media/recipe-R01_fig2.png打开.nc 文件" />

Figure 2: Sample file metadata from R-package “ncdf”.

4) Plotting an image

Sample script to plot an image (as in Figure 3):

#Load Plotting package

library(fields)

library(maptools)

data(wrld_simpl)

#Define min/max values to plot and colors for plotting

zmin=0.

zmax=20.

clevs<-c(0,2,4,6,8,10,12,14,16,18,20,50)

ccols<-c("#5D00FF", "#002EFF","#00B9FF","#00FFB9" ,"#00FF2E","#5DFF00","#E8FF00", "#FF8B00","red", "#FF008B","#E800FF")

palette(ccols)

#Plot image (see result in Figure 3)

par(mfrow=c(1,1))

image.plot(xlon,ylat,t(z), zlim=c(zmin,zmax), breaks=clevs, col=palette(ccols))

plot(wrld_simpl,add=TRUE)

To save the image as a PNG file:

par(mfrow=c(1,1))

png("image.png", width=700, height=500)

image.plot(xlon,ylat,t(z), zlim=c(zmin,zmax), breaks=clevs, col=palette(ccols))

plot(wrld_simpl,add=TRUE)

dev.off()

http://disc.sci.gsfc.nasa.gov/recipes/sites/default/files/media/recipe-R01_fig3.png打开.nc 文件" />

Figure 3: Sample screen shot of the R-Console window and the R-Graphics window.

source: http://disc.sci.gsfc.nasa.gov/recipes/?q=recipes/How-to-Read-Data-in-netCDF-Format-with-R

阅读┊ 收藏 ┊ 喜欢 ▼ ┊打印┊举报/Report

前一篇：r 清理控制面板

后一篇：在R中读取，查看数据

新浪BLOG意见反馈留言板　欢迎批评指正